Core practical write up 1.23

Core practical write up 1.23

Does caffeine affect heart rate?
To investigate the effect of caffeine on the heart rate of Daphnia (water fleas).
Caffeine is produced by plants as an insecticide.
Cocoa in South America, coffee in Africa and tea in Asia have all been used for hundreds of years to produce ‘pick me ups’ containing caffeine. These days caffeine is also used as a flavour enhancer in a wide range of cola and other soft drinks. In addition, it has medicinal uses in aspirin preparations and is found in weight loss drugs and as a stimulant in students’ exam time favourites like Pro plus and Red
Bull. In humans, caffeine acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, causing raised stress and blood pressure. This can lead to heart and circulation problems.


I predict that the concentration of caffeine will affect the Daphnia's heart rate. I believe this will be directly proportional to each other. For example, as concentration of caffeine in the blood increases, the heart rate of the daphnia will also increase. Caffeine is a drug that is classed as a stimulant because it stimulates the body's systems. It increases the activity of the neurotransmitters in your body which speeds up your heart rate, thus blood is pumped faster around the body.


The dependant variable being observed and measured was the number of heart beats per minute of the Daphnia (water flea), this will be measured by someone counting each beat and quickly making a mark on a piece of paper each time they see the Daphnia's heart beat. They will then count up how many marks there is on the paper and that will be the number of heart beats. The independent variable in this experiment was the concentrations of caffeine. Which were 0.1%, 0.2% and 0.3%. We did one test with 0% caffeine to see the...

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